I do not know how to relate the order number to voucher, is there any table that contains relation between voucher and order number. What changes are required to be done to this query for including order number. Please guide me in this query.
I am new to order management and AP.

I don't currently have access to a system and I may have misinterpreted something, but it appears to me that you are pulling back the order number (F.PO_ID). My understanding is that Order Management relates to the supply of goods and therefore the Billing module (Order to Cash process stream), while the order number for a purchase order relates to the purchase of goods and services (Purchasing Module) and though to the Payables module (Procure to Pay process stream). The fact that you have got the PO_ID joined to the VOUCHER_LINE record seems appropriate to me, meaning you are getting the PO number from the lowest level.

I suggest you go back and get more info. What exactly are you tying together from the two areas?

As Neil states, OM and AP follow 2 very different paths. The only two connections I can think of is via Inventory/Purchasing and the refunding on an order. Trying to connect the two via Inventory purchases is might prove to be tricky, and for refunds I don't see how unless your A/P dept is entering something in the voucher to tie the two together (at least the way we do it, that is)